1. Field of the Invention
The present invention relates to the field of semiconductor devices, and more particularly, to a molding apparatus and method by which, when a molding compound is injected into a mold to encapsulate simultaneously a plurality of semiconductor devices, abnormal operation of the molding apparatus is detected.
2. Discussion of Related Art
In assembling semiconductor devices, a molding process encapsulates semiconductor devices using a molding compound such as epoxy molding compound (hereinafter “EMC”) to mold the semiconductor devices into packages. Preferably, prior to the molding process, a lead connection process bonds the semiconductor devices to a lead frame. This molding process is performed in a mass-production process to mold a large number of semiconductor devices at the same time by an automatic molding apparatus. Generally, the molding of a large number of semiconductor devices bonded to a lead frame is automatically repeated.
To mold a large number of semiconductor devices, a molding apparatus includes a plunger block or a plunger unit having a plurality of plungers. The plunger block generally includes about 10 plungers or less. The plungers are plunged into a mold to inject a molding compound into the mold. Here, the individual plungers move along with the movement of the plunger block so as to inject the molding compound into the mold.
When the plungers ascend from below the mold into the mold to inject the molding compound into the mold, the plungers in the plunger block ascend not separately but simultaneously with the ascent of the plunger block. With the application of such a plunger block type press, uniform pressure can be applied when molding a plurality of semiconductor devices at the same time.
However, when occasionally one or more of the plungers does not operate properly, such as a plunger does not completely ascend even though the plunger block completely ascends, the molding compound will not be completely injected into the mold, and thus the molding of a semiconductor device corresponding to the specific plunger may be incomplete. Further, if the ascent of the specific plunger is incomplete, excessive pressure may be applied on the specific plunger and further molding failures occur.
FIG. 1 is a cross-sectional view of a molding apparatus in which semiconductor devices are normally molded. FIG. 2 is a cross-sectional view of a molding apparatus in which semiconductor devices are incompletely molded.
Referring to FIG. 1, as a plunger block (not shown) ascends, a plunger 10 ascends into a plunger hole 27 formed into a mold 20. A molding compound 40, e.g., epoxy molding compound (EMC), which is placed on the plunger 10 and being melted into liquid, flows into molding cavities 25 in the mold 20 due to pressure generated by the ascent of the plunger 10. Here, the plunger 10 ascends with a predetermined pressure to inject the molding compound 40. The molding cavities 25 are formed in a predetermined shape between a lower mold 21 and an upper mold 23 to form molding products or packages 50 in a predetermined shape. The molding compound 40 is injected where a lead frame 30, to which semiconductor devices are bonded by a lead connection process, is installed in the molding cavities 25.
When the plunger 10 ascends completely, the liquid molding compound 40 smoothly flows into the molding cavities 25 and completely fills the molding cavities 25. Thereafter, the molding compound 40 is fully solidified to complete the molding products 50. Next, the plunger 10 descends, the lower and upper molds 21 and 23 are separated from each other, and the molding products 50 are taken away.
To normally complete the molding products 50, the plunger 10 must smoothly and completely ascend into and descend out of the mold 20 along with the plunger block. However, although the plunger block normally ascends, there is a case where one or more plunger in the plunger block may not normally ascend for several reasons.
Referring to FIG. 2, if a plunger 15 in a plunger block does not normally ascend into a mold 20 even in a case where the plunger block normally ascends, the molding compound 40 cannot smoothly and fully flow into molding cavities 25 in the mold 20 because the plunger 15 fails to apply full pressure to a molding compound 40. As a result, the molding cavities 25 are not completely filled with the molding compound 40 and molding products 55 are poorly completed. For example, semiconductor devices 31, which are placed on and electrically connected to a lead frame 30 by bonding wires 33, are incompletely encapsulated.
Such poor molding occurs mainly when the plunger 15 does not normally ascend due to abnormal friction with the sidewall of a plunger hole 27 even though the plunger block normally ascends. Then, the plunger 15 stops ascending, and thus incomplete injection or incomplete molding occurs.
The stopping or abnormal operation of the plunger block can be sensed or detected when all of the plungers or a great majority of plungers in the plunger block simultaneously stop or abnormally operate. However, the abnormal operation of a small number of plungers in the plunger block does not greatly affect the movement of the plunger block, and thus the abnormal operation may not be detected. In other words, in a plunger block type press, since the movement of the plunger block causes the plungers to move together, there may be a certain specific plunger operating abnormally even when the plunger block moves normally. Thus, it is difficult to individually sense the abnormal operations of certain specific plungers.
Since semiconductor devices molding is continuously repeated in an automatic molding apparatus for mass-producing semiconductor devices, if the abnormal operations of specific plungers cannot be detected, a large number of molding may be poor. In particular, as chip sizes of semiconductor devices become smaller, a plurality of molding cavities (25 of FIG. 1) are designed to correspond to one plunger (10 of FIG. 1) to improve productivity. Thus, if the abnormal operation of the plunger 10 is not sensed quickly or in real-time, a large number of poorly molded semiconductor devices may result. Also, if the abnormal operation of the specific plunger continues, not only will semiconductor devices be poorly molded, but the abnormal operation will also spread over the mold to perhaps the entire automatic molding apparatus.
Therefore, a method or a molding apparatus is needed by which molding products can be efficiently prevented from being poorly manufactured, by separately detecting the abnormal operations of individual plungers in real-time during a molding process.